Gradient Methylidene-Ethylidene Copolymer via C1 Polymerization: an Ersatz Gradient Ethylene-Propylene Copolymer.

We report the first synthesis of a gradient methylidene-ethylidene copolymer via a living C1 polymerization. The copolymer has a similar chemical structure as the corresponding ethylene-propylene copolymer. To achieve this goal a new and convenient source of the ethylide monomer, diethylsulfoxonium ethylide, was developed for the introduction of the methyl branch in the polymer backbone. The gradient copolymer contains a gradual change of instantaneous methyl branch content from 0% on one end of the polymer chain to 63% on the other end. Thermal analysis revealed that the gradient copolymers have a narrow glass transition temperature range with values intermediate between those of linear polyethylene and atactic polypropylene.